We present an experimental study of the high-energy excitation spectra of unitary Fermi gases. Using focused beam Bragg spectroscopy, we locally probe atoms in the central region of a harmonically ...trapped cloud where the density is nearly uniform, enabling measurements of the dynamic structure factor for a range of temperatures both below and above the superfluid transition. Applying sum rules to the measured Bragg spectra, we resolve the characteristic behavior of the universal contact parameter, C, across the superfluid transition. We also employ a recent theoretical result for the kinetic (second-moment) sum rule to obtain the internal energy of gases at unitarity.
A Bose-Einstein condensate is used as an atomic source for a high precision sensor. A 5×10^{6} atom F=1 spinor condensate of ^{87}Rb is released into free fall for up to 750 ms and probed with a ...T=130 ms Mach-Zehnder atom interferometer based on Bragg transitions. The Bragg interferometer simultaneously addresses the three magnetic states |m_{f}=1,0,-1⟩, facilitating a simultaneous measurement of the acceleration due to gravity with a 1000 run precision of Δg/g=1.45×10^{-9} and the magnetic field gradient to a precision of 120 pT/m.
We present the first realization of a solitonic atom interferometer. A Bose-Einstein condensate of 1×10(4) atoms of rubidium-85 is loaded into a horizontal optical waveguide. Through the use of a ...Feshbach resonance, the s-wave scattering length of the 85Rb atoms is tuned to a small negative value. This attractive atomic interaction then balances the inherent matter-wave dispersion, creating a bright solitonic matter wave. A Mach-Zehnder interferometer is constructed by driving Bragg transitions with the use of an optical lattice colinear with the waveguide. Matter-wave propagation and interferometric fringe visibility are compared across a range of s-wave scattering values including repulsive, attractive and noninteracting values. The solitonic matter wave is found to significantly increase fringe visibility even compared with a noninteracting cloud.
We present an experimental and theoretical study of the phonon mode in a unitary Fermi gas. Using two-photon Bragg spectroscopy, we measure excitation spectra at a momentum of approximately half the ...Fermi momentum, both above and below the superfluid critical temperature T_{c}. Below T_{c}, the dominant excitation is the Bogoliubov-Anderson (BA) phonon mode, driven by gradients in the phase of the superfluid order parameter. The temperature dependence of the BA phonon is consistent with a theoretical model based on the quasiparticle random phase approximation in which the dominant damping mechanism is via collisions with thermally excited quasiparticles. As the temperature is increased above T_{c}, the phonon evolves into a strongly damped collisional mode, accompanied by an abrupt increase in spectral width. Our study reveals strong similarities between sound propagation in the unitary Fermi gas and bosonic liquid helium.
We apply an online optimization process based on machine learning to the production of Bose-Einstein condensates (BEC). BEC is typically created with an exponential evaporation ramp that is optimal ...for ergodic dynamics with two-body s-wave interactions and no other loss rates, but likely sub-optimal for real experiments. Through repeated machine-controlled scientific experimentation and observations our 'learner' discovers an optimal evaporation ramp for BEC production. In contrast to previous work, our learner uses a Gaussian process to develop a statistical model of the relationship between the parameters it controls and the quality of the BEC produced. We demonstrate that the Gaussian process machine learner is able to discover a ramp that produces high quality BECs in 10 times fewer iterations than a previously used online optimization technique. Furthermore, we show the internal model developed can be used to determine which parameters are essential in BEC creation and which are unimportant, providing insight into the optimization process of the system.
We present an experimental study of a two component Fermi gas following an interaction quench into the superfluid phase. Starting with a weakly attractive gas in the normal phase, interactions are ...ramped to unitarity at a range of rates and we measure the subsequent dynamics as the gas approaches equilibrium. Both the formation and condensation of fermion pairs are mapped via measurements of the pair momentum distribution and can take place on very different timescales, depending on the adiabaticity of the quench. The contact parameter is seen to respond very quickly to changes in the interaction strength, indicating that short-range correlations, based on the occupation of high-momentum modes, evolve far more rapidly than the correlations in low-momentum modes necessary for pair condensation.
Flooding affects more people than any other environmental hazard and hinders sustainable development. Investing in flood adaptation strategies may reduce the loss of life and livelihood caused by ...floods. Where and how floods occur and who is exposed are changing as a result of rapid urbanization4, flood mitigation infrastructure and increasing settlements in floodplains6. Previous estimates of the global flood-exposed population have been limited by a lack of observational data, relying instead on models, which have high uncertainty. Here we use daily satellite imagery at 250-metre resolution to estimate flood extent and population exposure for 913 large flood events from 2000 to 2018. We determine a total inundation area of 2.23 million square kilometres, with 255–290 million people directly affected by floods. We estimate that the total population in locations with satellite-observed inundation grew by 58–86 million from 2000 to 2015. This represents an increase of 20 to 24 per cent in the proportion of the global population exposed to floods, ten times higher than previous estimates. Climate change projections for 2030 indicate that the proportion of the population exposed to floods will increase further. The high spatial and temporal resolution of the satellite observations will improve our understanding of where floods are changing and how best to adapt. The global flood database generated from these observations will help to improve vulnerability assessments, the accuracy of global and local flood models, the efficacy of adaptation interventions and our understanding of the interactions between landcover change, climate and floods.
According to the 'hygiene hypothesis', the decreasing incidence of infections in western countries and more recently in developing countries is at the origin of the increasing incidence of both ...autoimmune and allergic diseases. The hygiene hypothesis is based upon epidemiological data, particularly migration studies, showing that subjects migrating from a low-incidence to a high-incidence country acquire the immune disorders with a high incidence at the first generation. However, these data and others showing a correlation between high disease incidence and high socio-economic level do not prove a causal link between infections and immune disorders. Proof of principle of the hygiene hypothesis is brought by animal models and to a lesser degree by intervention trials in humans. Underlying mechanisms are multiple and complex. They include decreased consumption of homeostatic factors and immunoregulation, involving various regulatory T cell subsets and Toll-like receptor stimulation. These mechanisms could originate, to some extent, from changes in microbiota caused by changes in lifestyle, particularly in inflammatory bowel diseases. Taken together, these data open new therapeutic perspectives in the prevention of autoimmune and allergic diseases.
Composite materials are designed in order to combine the favorable properties of their components. For technical applications of these materials the determination of their effective material and ...fracture mechanical properties is of great interest. The study of fracture of heterogeneous composite materials, which is a necessary first step in order to derive effective fracture mechanical properties, is a difficult topic since macroscopic failure is usually accompanied by various fracture events on the microstructural scale. Finite element implementations of phase field fracture models enable the simulation of complex fracture scenarios as they occur in fracturing of heterogeneous materials. An adaption of the configurational force concept from linear elastic fracture mechanics to the phase field model provides more insight into the mechanisms underlying the evolution of fracture. In this work this ansatz is used to study the interplay between local crack driving forces and the evolution of fracture. Furthermore, the effects of the microstructure on macroscopically measurable quantities like the far field J-integral are analyzed in representative examples comprising continuously modulated as well as layered structures with varying stiffness and varying cracking resistance.
Background
Trichomoniasis commonly affects women of childbearing age and has been linked to several adverse birth outcomes.
Objective
To elucidate the association between trichomoniasis in pregnant ...women and adverse birth outcomes, including preterm delivery, prelabour rupture of membranes and low birthweight.
Search strategy
MEDLINE, EMBASE and ClinicalTrials.gov were systematically searched in December 2020 without time or language restrictions.
Selection criteria
Original research studies were included if they assessed at least one of the specified adverse birth outcomes in pregnant women with laboratory‐diagnosed trichomoniasis.
Data collection and analysis
Estimates from included articles were either extracted or calculated and then pooled to produce a combined estimate of the association of trichomoniasis with each adverse birth outcome using the random effects model. Heterogeneity was assessed using the I2 statistic and Cochran's Q test.
Main results
Literature search produced 1658 publications after removal of duplicates (n = 770), with five additional publications identified by hand search. After screening titles and s for relevance, full text of 84 studies was reviewed and 19 met inclusion criteria for meta‐analysis. Significant associations were found between trichomoniasis and preterm delivery (OR 1.27; 95% CI 1.08–1.50), prelabour rupture of membranes (OR 1.87; 95% CI 1.53–2.29) and low birthweight (OR 2.12; 95% CI 1.15–3.91).
Conclusions
Trichomoniasis in pregnant women is associated with preterm delivery, prelabour rupture of membranes and low birthweight. Rigorous studies are needed to determine the impact of universal trichomoniasis screening and treatment during pregnancy on reducing perinatal morbidity.
Tweetable
This systematic review and meta‐analysis found that in the setting of pregnancy, trichomoniasis is significantly associated with multiple adverse birth outcomes, including preterm delivery, low birthweight, and prelabour rupture of membranes.
Tweetable
This systematic review and meta‐analysis found that in the setting of pregnancy, trichomoniasis is significantly associated with multiple adverse birth outcomes, including preterm delivery, low birthweight, and prelabour rupture of membranes.
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